1. Field of the Invention
This invention relates in general to bending presses or similar machine tools comprising two beams overlying each other in substantially co-planar relationship and disposed on either side of the working bed, one beam being fixed and the other vertically movable.
2. Description of the Prior Art
In the case of a bending press, one beam carries the punch and the other beam carries the die of the bending tool.
However, to bend sheet plate while maintaining a constant angle throughout the length of the fold, the punch must engage the die to the same extent or depth throughout its length. Now, this penetration is controlled inter alia by the following parameters:
ON THE ONE HAND, THE POSITION OF THE MOVABLE BEAM IN RELATION TO THE FIXED BEAM AT THE END OF THE BENDING OPERATION, THIS POSITION DETERMINING THE AVERAGE ANGLE OF THE FOLD, AND
ON THE OTHER HAND, THE DIFFERENCE BETWEEN THE DISTORTIONS OF THE TWO BEAMS, WHICH GIVES THE ANGULAR VARIATIONS ABOUT THE AVERAGE ANGLE, THUS INVOLVING A LACK OF PRECISION.
The main difficulty is due to the fact that the sheet metal reacts on both beams with uniformly distributed forces exerted in opposite directions. Now, in bending presses or similar machines wherein the fixed beam is supported at its ends, in contrast to the movable beam actuated by driving members also located at its ends, the working edges of the two beams are flexion-stressed in opposite directions. As a result, considerable irregularities or unevennesses are observed along the fold.
To avoid this serious inconvenience, the movable beam of certain known presses is actuated either by a single hydraulic cylinder disposed in the transverse median plane of the beam, or by a plurality of cylinders disposed symmetrically in relation thereto. Thus, a central thrust can be exerted on the movable beam, so that the flexion of the registering edges of the two beams takes place in the same direction. Consequently, a compensation is obtained between the distortions of both beams, so that the above-mentioned inconveniences can be at least partially avoided. However, though this solution is very advantageous in comparison with the first type of machine mentioned hereinabove, it is objectionable in that it gives different distortion curves between the working edges of the two beams. This is due to the difference arising in the distribution of the applied efforts.
Moreover, in the case of hydraulic balance means, this solution makes it necessary to provide at the ends of the movable beam a pair of balancing hydraulic cylinders having a crossed interconnection. The only function of these cross-connected cylinders is to exert a parallel guiding action on the movable beam, irrespective of the distribution of overhanging bending forces, these cylinders playing no part in the sheet bending operation.